Net Income (Loss) per Share - Computation of Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator
Net income (loss)	$ 6,782	$ 3,475	$ (73,023)	$ (29,756)
Weighted average shares:
Basic (in shares)	91,994,731	87,743,223	91,279,086	84,327,266
Dilutive shares from stock plans (in shares)	5,176,539	6,899,240	0	0
Dilutive (in shares)	97,171,270	94,642,463	91,279,086	84,327,266
Net income (loss) per share
Net income (loss) per share - basic (in dollars per share)	$ 0.07	$ 0.04	$ (0.80)	$ (0.35)
Net income (loss) per share - diluted (in dollars per share)	$ 0.07	$ 0.04	$ (0.80)	$ (0.35)